Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 35 replies
  • Subscribers 31 subscribers
  • Views 4640 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Appendix 4, section 6.1 equation 6

Former Community Member
Former Community Member

 

85b1fc637cfb5e3825ed2b73d8b54527-original-image.png

Hi I am working through equation 6 for an ambient temperature of 50 degrees for 1mm 90degC thermoplastic cable (Table 4E2A)

11d17c7d56aee28e7d23803363b44f10-original-image.png

I get a correction factor of 0.95 for a 2A load. 

Do i divide the mV/A/m by this factor ? 

The text says multiply, but that would mean the resistance decreases with the increase in temperature (or have I got the sum wrong?)

Parents
  • 0

    I'd just round up the 0.952619 to 1.0 and call it a day. We ain't that precise in the real world of chucking in cables and “power” electrics.

    Please read the last paragraph on page 381.

    Also, please read the NOTE in 6.1 regarding the APPROXIMATE  resistance temperature coefficient. The calculation is very approximate.

    Quite so. As something of a collector of rules of thumb, I'm inclined to agree.  Often we seem to calculate by computer, measure with micrometer, mark in chalk, cut with an axe…

    There is another way to check, the rule of 16, which is even more approximate. Namely that a single core 1mm cross -section and is 16 milliohms per metre at room temp (more like 19 when running hot) so if you had 300m each way in  2.5mm2, you may expect 3.8 ohms or so cold rising to more like 4.2 ohms when hot.  So turning the question around, Is an 8 volt drop at full load going to stop the party?

    Mike.

Reply
  • 0

    I'd just round up the 0.952619 to 1.0 and call it a day. We ain't that precise in the real world of chucking in cables and “power” electrics.

    Please read the last paragraph on page 381.

    Also, please read the NOTE in 6.1 regarding the APPROXIMATE  resistance temperature coefficient. The calculation is very approximate.

    Quite so. As something of a collector of rules of thumb, I'm inclined to agree.  Often we seem to calculate by computer, measure with micrometer, mark in chalk, cut with an axe…

    There is another way to check, the rule of 16, which is even more approximate. Namely that a single core 1mm cross -section and is 16 milliohms per metre at room temp (more like 19 when running hot) so if you had 300m each way in  2.5mm2, you may expect 3.8 ohms or so cold rising to more like 4.2 ohms when hot.  So turning the question around, Is an 8 volt drop at full load going to stop the party?

    Mike.

Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines